The Enhancement Of Silicon Anodes Performance By 3D Network Binder And High-concentration Electrolyte

Graphite,the traditional anode material which is widely used in Lithium-ion batteries(LIBs),has become a bottleneck for increasing the energy density of LIBs due to its low theoretical capacity of 372 mAh g-1.While silicon-based anodes are considered as the greatest potential anode materials for next-generation LIBs owing to their relatively high specific capacities and low charge/discharge platforms.However,silicon-based anodes have a series of problems,such as large volume expansion during cycling,unstable solid electrolyte interfaces(SEI)layer,and low initial Coulombic efficiency(ICE),which greatly limit the large-scale application of silicon-based anodes.In respect of the issues above,the performance of silicon anode is improved by 3D network binder and high-concentration electrolyte in this thesis.As a widely used water-based binder,sodium alginate(SA)shows good performance when used in nano-silicon(n-Si)electrode,but its shows poor performance when it is applied to micro-silicon(m-Si)electrode.For this reason,we fill up the pores of S A network with lithiated polyacrylic acid(LixPAA)to form a threedimension cross-linked bicontinuous composite network binder(b-Li0.5PAA@SA),in which the pores of the SA skeleton are dominated with the Li0.5PAA domains;within such composite the SA and Li0.5PAA interlock tightly each other via extensive interfacial ester bonding after 150℃ heated.The b-Li0.5PAA@S A network binder can greatly improve the cycle performance of the m-Si electrode.After 150 cycles,the specific capacity of m-Si/b-Li0.5PAA@SA electrode is 2762 mAh g-1 with the capacity retention rate of 50.8%.Cyclic voltammetry(CV),electrochemical impedance spectroscopy(EIS)and scanning electron microscopy(SEM)have proved that the bLi0.5PAA@SA binder network can effectively inhibit the reduction of electrolyte,reduce electrochemical impedance and maintain a high structural integrity of electrodes after cycling.At the same time,in order to stabilize the SEI layer and improve the coulombic efficiency of the silicon anode,a tetrahydrofuran-based high-concentration electrolyte(HCE)is designed.When the molar ratio of tetrahydrofuran(THF)to lithium bis(fluorosulfonyl)imide(LiFSI)is 14:5,the silicon-based electrodes show best cycle performance in as prepared 14THF-5LiFSI electrolyte.After 200 cycles,the specific capacity of n-Si electrode is 1471.1 mAh g-1 with the capacity retention of 69.5%,which is much higher than traditional ester-based electrolytes(35.8%).In addition,linear sweep voltammetry(LSV)results show that the decomposition potential of 14THF5LiFSI electrolyte reaches 4.7 V,which basically meets the requirements of commercial cathode materials.The characterization proved that the 14THF-5LiFSI electrolyte can make SEI film more stable and thinner,also reduce the fracture of n-Si electrode during the cycle,indicating that the tetrahydrofuran-based HCE has a good application prospect in the silicon anode.